1. Field of the Invention
The present invention relates to a film thickness measuring method measuring a film thickness of an element formation film formed on a substrate, a fabrication method of a thin film magnetic head having a planarization process for polishing and planarizing a surface of material to be polished and a substrate for forming a thin film magnetic head which forms a plurality of elements structuring the thin film magnetic head.
2. Description of the Related Art
In a fabrication of a thin film magnetic head used as a head for writing/reading of a magnetic disk drive, a chemical mechanical polishing (hereinafter, referred to a CMP) is used when a surface having a high flatness is formed. In the CMP, first, a polishing surface of a polishing pad covered on the rotating polishing surface plate and a surface to be polished of a substrate which is a material to be polished held on a polishing head are contacted with pressure. Then, supplying slurry, which is an abrasive material, on the polishing surface of the polishing pad, and respectively rotating the polishing pad and the polishing head, the slurry is supplied between the polishing pad and the surface to be polished, thereby polishing the surface to be polished chemically and mechanically. By this polishing using the CMP, a desired global flatness can be obtained along with a local flatness.
In the meantime, in a planarization process by a surface polishing using this CMP, it is extremely important, in a point to decide a performance of the completed elements, to control the polishing so that a polishing object film after polishing has a predetermined residual film thickness. Therefore, how to be able to measure the residual film thickness of the polishing object film at a high accuracy is a subject for a planarization process of the CMP.
In the past, a non-contact and contact film thickness measuring equipments have been used for the measurement of the residual film thickness of the polishing object film. As the non-contact film thickness measuring equipments, an optical film thickness measuring equipment named NanoSpec (product name: made by Nanometrics Japan), for example, exists. This non-contact optical film thickness measuring equipment inputs light to the film to be measured and then measures the film thickness of the film to be measured based on interference between a light reflected on the surface of the film to be measured and a light which transmits through the film to be measured and is reflected on the surface of a lower layer.
FIG. 10 shows a measuring method of the residual film thickness using the above non-contact optical film thickness measuring equipment in a process in the midst of a fabrication process of the thin film magnetic head. FIG. 10(a) shows a rough state viewing an element 101 formed on the substrate from the top of the substrate. FIG. 10(b) shows a cross section cut by a line Axe2x80x94A in FIG. 10(a). First, a structure of the element 101 in the midst of the formation illustrated is briefly described. A bottom shielding layer 104 which is made of permalloy (NiFe), for example, and planarized by using the CMP is formed on an AlTiC substrate 102. Though a description is omitted, an MR reading element and an insulating layer sandwiching the MR reading element are formed on the bottom shielding layer 104. Then, a top shielding layer (a bottom pole: a bottom magnetic pole) 106 is formed by laminating and patterning permalloy on this insulating layer. Further, after embedding and coating the top shielding layer with alumina, a planarization is performed using the CMP. Then, a planarized layer made of the top shielding layer 106 and embedded layers 108 and 108xe2x80x2 is formed.
In the meantime, a method for measuring the film thickness of the top shielding layer 106 formed as above by the non-contact optical film thickness measuring equipment is briefly described. A light beam formed by setting down a spot diameter 110 to approximately 20 xcexcm is irradiated to the embedded layer 108 from this film thickness measuring equipment. A part of the light beam is reflected on the surface of alumina of the embedded layer 108xe2x80x2 and the rest of the light transmits through the transparent alumina and is reflected on the surface of the bottom shielding layer 104. The film thickness measuring equipment measures a film thickness of the embedded layer 108xe2x80x2 by receiving and making these both reflection lights interfere. Since the upper surface of the bottom shielding layer 104 is planarized by the CMP and the top shielding layer 106 and the embedded layers 108 and 108xe2x80x2 are planarized by the CMP as well, the film thickness of the embedded layer 108xe2x80x2 shows the film thickness of the top shielding layer 106. It will be noted that the film thickness of the insulating layer on the bottom shielding layer 104 is extremely so thin that the film thickness of the insulating layer on the bottom shielding layer 104 can be neglected or can be of course obtained as the top shielding layer 106 by reducing the known film thickness of the insulating layer from the measured value.
Thus, in the conventional film thickness measurement, the measurement is performed by irradiating the light beam of the non-contact optical film thickness measuring equipment on the surface in the element area during the formation. However, the recording density of the recent magnetic recording device is more and more improved, and finer and more complicated elements structuring the thin film magnetic head are further progressed along with this improvement. Therefore, it becomes more difficult to find a preferable position for the measurement on the element. In some case, the spot diameter 110 of the non-contact optical film thickness measuring equipment can not be fully entered in the irradiation area of the surface of the element during the formation. A portion of the light beam goes beyond the measurement area, thereby leading to a problem that the enough irradiation for the measurement is more difficult. As described above, the spot diameter 110 of the light beam described in FIG. 10 is currently equal to approximately 20 xcexcm. On the other hand, a dimension W3 of the embedded layer 108xe2x80x2 in the measurement area shown in FIG. 10 is proceeded to be fined under 20 xcexcm. If the current spot diameter is further reduced to accept the request of finer elements, a time is consumed for a positional confirmation before the measurement in the relationship with a measurement positioning accuracy, so that the reduction of the spot diameter is undesirable in mass-production because consequently a time required for the measurement becomes longer. If this problem is to be solved, the technical and cost burden for the film thickness measuring equipment increases, thereby leading to a higher cost of the thin film magnetic head.
Thus, in the conventional film thickness measuring method, a problem that the measurement of the residual film thickness in the polishing process such as the CMP becomes difficult accompanying to the finer and more complicated elements. Further, the difficulty of the film thickness measurement gives an influence on the mass-productivity of the elements. The more the difficulty of the film thickness measurement increases, the more a reduction of a yield in element fabrication is created. Furthermore, a throughput of the element fabrication is reduced because the time required for the film thickness measurement increases in the fabrication process, thereby leading to a possibility to create the quantity reduction of product supply.
An object of the present invention is to provide a film thickness measuring method which can measure a residual film thickness of a polishing object film in a polishing process at a high accuracy.
Another object of the present invention is to provide a film thickness measuring method which can measure a film thickness at a high accuracy even if a measurement area of the residual film thickness of the polishing object film in the polishing process is fined.
Further object of the present invention is to provide a polishing method and a fabrication method of a thin film magnetic head which improve a yield of a element fabrication by measuring a residual film thickness of a polishing object film in a polishing process at a high accuracy.
Furthermore object of the present invention is to provide a substrate for forming a thin film magnetic head which can form a plurality of elements, which structures a thin film magnetic head by the fabrication method of the above thin film magnetic head, at a high accuracy.
The above objects are achieved by a method of measuring a film thickness comprising the steps of forming, on the substrate, an element formation layer structuring a portion of an element and at least one dummy layer for a film thickness measurement which has a predetermined film thickness thinner than the element formation film and does not contribute to the structure of the element, forming a planarized layer planarized by polishing a surface until the surface of the element formation layer exposes from a embedded layer, after embedding and coating the element formation layer and the dummy layer with a predetermined embedding material, measuring a film thickness of the embedded layer over the dummy layer, and measuring a film thickness of the element formation layer based on the film thickness of the embedded layer. Further, in a film thickness measuring method in the present invention, the dummy layer is simultaneously formed with an alignment mark for an alignment on the substrate when the alignment mark is formed. Further, the dummy layer is made of a material which reflects light on the surface thereof. Further, the material is metal.
Further, the above objects are achieved by a method of measuring a film thickness comprising the steps of forming, on a surface, a first element formation layer structuring a portion of an element and at least one dummy layer which does not contributes to the structure of the element, forming a first planarized layer planarized by polishing a surface until a surface of the first element formation layer and the surface of the dummy layer expose after embedding and coating the first element formation layer and the dummy layer, forming a second element formation layer structuring a portion of the element on the first planarized layer; forming a second planarized layer planarized by polishing a surface until the surface of the second element formation layer exposes from the embedded layer after embedding and coating the second element formation layer with a predetermined embedding material, measuring a film thickness of the embedded layer on the dummy layer, and measuring a film thickness of the second element formation layer based on the film thickness of the embedded layer.
In a film thickness measuring method of the present invention, the first element formation layer and the dummy layer are simultaneously formed in the same process. Further, in a film thickness measuring method of the present invention, a plurality of the dummy layers are provided on a reference layer of a film thickness measurement according to the number of layers the thickness of which are measured. Further, in a film thickness measuring method of the present invention, at least one second dummy layer is formed when the second element formation layer is formed. Further, in a film thickness measuring method of the present invention, the second element formation layer and the second dummy layer are simultaneously formed in the same process.
In a film thickness measuring method of the present invention described above, the second dummy layer is laminated over the dummy layer of the first planarized layer. Further, the planarized layer is formed by polishing a surface using a chemical mechanical polishing.
Further, in a film thickness measuring method of the present invention, an area of the upper surface of the dummy layer is formed to be larger than one portion of an area of the element structured at the element formation layer. Then, in a film thickness measuring method of the present invention described above, the film thickness of the embedded layer is measured based on interference between a light reflected on the surface of the embedded layer when inputting a light to the embedded layer and a light transmitting through the embedded layer and reflected on the surface of the dummy layer.
Further, above objects are achieved by a fabrication method of a thin film magnetic head comprising a planarization process for polishing and planarizing a surface of a material to be polished wherein the planarization process uses the film thickness measuring method described above. In a fabrication method of a thin film magnetic head of the present invention, the first element formation layer structures a bottom shielding layer of the thin film magnetic head and the second element formation layer structures a top shielding layer of the thin film magnetic head.
Further, in a fabrication method of a thin film magnetic head of the present invention, the transparent insulating material is used as a predetermined embedding material. Further, the insulating material is alumina.
Further, above objects are achieved by a polishing method for polishing the surface of a material to be polished to planarize the material at a predetermined film thickness comprising the step of using the method of measuring a film thickness described above when measuring the predetermined film thickness.
Furthermore, above objects are achieved by a substrate for forming a plurality of elements structuring the thin film magnetic head comprises a dummy layer which is formed for being used in the method of measuring a film thickness described above.